AeroElectric-List Digest Archive

Thu 10/05/17


Total Messages Posted: 7



Today's Message Index:
----------------------
 
     1. 10:06 AM - Re: Re: Voltmeter & Ammeter normal ranges (Robert L. Nuckolls, III)
     2. 11:24 AM - Daily List Digest Question (jrevens)
     3. 01:57 PM - Re: Dual batteries or dual alternators? (Flying Patagonia)
     4. 03:46 PM - Re: Dual batteries or dual alternators? (Flying Patagonia)
     5. 06:38 PM - alternator whine (Alec Myers)
     6. 07:39 PM - Re: alternator whine (user9253)
     7. 10:05 PM - Re: Re: Voltmeter & Ammeter normal ranges (Bob Verwey)
 
 
 


Message 1


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    Time: 10:06:38 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: Voltmeter & Ammeter normal ranges
    At 08:32 AM 9/24/2017, you wrote: >Exactly. Joe could you please confirm that the jpeg below is >visible? If so it's obvious that while the voltage seems to be >moving around a tiny bit, it never gets to the point which would >allow the amperage shown. It's always above 14V. Also I checked some >data with the engine shut down and while the amperage still wanders >around it's 1 A or less (-5.5 to -6.5 A) Digital data acquisition is fraught with opportunity for confusion/error. Depending on how the variable is sampled, pre-filtered and software filtered, data displayed or plotted can take on the appearance of instability. Unless you're measuring the output from something like a battery . . . or a laboratory power supply, the stimulus being observed will have some noise on it. This is especially true of signals gathered from the DC power system of any vehicle. When I'm gathering data on relatively low frequency events, my DAS pre-filtering is usually rolled off at 10 Hz. Then interpretation software is designed to do a 'rolling average' on sampled values. For a DAS set up to gather 100 samples/second, we'll buffer 16 samples in a memory stack, take the sum of those values then divide by 16 for an average of that 'packet' of data. When the next sample comes in, we add the new value, throw away the oldest value and do the average again. This pre/post processing of data does a nice job of ignoring the high frequency perturbations that are riding on top of the value of interest. The processed data plots are nice smooth lines that are more meaningful. I suspect that data plots taken from most EIS systems have little pre-processing and no post processing . . . so the traces are understandably 'ragged'. So while the voltage traces might be interpreted as 'unstable', it's probable that the system is operating normally. Just for grins, I took the 'scope out to peek at the 14v bus in Dr. Dee's '87 GMC Sierra. With the 'scope set to 2.5S/div H and 2V/div V, we get the following trace when cranking the engine. [] Figure 1. Note that battery voltage starts to sag from about 12.8 volts but takes a steeper slope as the starter contactor is energized followed by a profound drop to 8 volts as the contactor closes. A few milliseconds later, the voltage rises to about 10v until the engine catches approx 1.2S later and the alternator kicks in . . . whereupon but bus rises to about 14.6V [] Figure 2. In the next plot we see that the bus is 'steady' at about 14.7V with the occasional perturbation combined with some little 'spikes' with an amplitude of 1 to 2 volts. To get a closer look at the voltage in the next plot, we need to turn up the 'scope sensitivity and to to AC coupling: [] Figure 3. With a vertical scale of 0.5V/div and horizontal of 0.05S/div we can get a better look at the 'noise'. This particular trace caught a 1.5v transient amongst about 10 smaller artifacts. We see that even when there are no obvious transients, the horizontal line has 'thickness'. Zooming in closer: [] Figure 4. We find that the horizontal line is 'fuzzy' with positive and negative going transients on the order of 300mV peak. Depending on where your digital data acquistion system takese a 'snapshot', the sampled votlage might appear to 'wobble' by as much as +/-0.5V. Spreading out the major transients by a factor of 20 . . . [] Figure 5. Shows that they're about 400 microSeconds wide. These plots offer a small peek into the nature of DC power systems on vehicles. A few weeks ago, a thread on another list server offered this image suggesting that the full-wave, rectified 3-phase alternator would produce wave forms something along these lines . . . [] Figure 6. Theoretically true, but I've never seen so 'clean' a picture in the wild . . . Referring to Mil-Std-704 we learn that DC power systems demonstrate a certain amount of noise (distortion) under normal conditions. The document cites the following plot for a 28v system (cut the numbers in half for 14 volts). [] Figure 7. Over the range of 1000 Hz (1 milliSecond period) and 10,000 Hz (100 uSecond), we should expect artifacts of noise up to 0.5 VRMS (1.5 volts pk-pk) on a 14V bus. Above and below those frequencies, the allowable/exoected noise levels fall off. When you hook an oscilloscope to the bus, the best you can do is sample small features of the noise as illustrated in the first 5 figures. Further, you'll never see the pristine plots hypothesized in Figure 6. Emacs! Figure 8. The most significant attribute of a DC power system is VOLTAGE. Referring again to Mil-STD-704 we find the plot above. Again, cut the voltage levels in half for a 14v system. This figure suggests that any voltage vs. time condition below the upper trace . . . and above the lower trace . . . is a condition to be expected for designing and operating appliances powered from the DC system. It's my wish that this narrative will give you some tools for critical review of any data presented by either operating or diagnostic instruments. Understanding characteristics signals present on the bus -AND- limits on the measuring instrument will go to better design, operation and diagnosis of your ship's DC power system. Bob . . .


    Message 2


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    Time: 11:24:13 AM PST US
    Subject: Daily List Digest Question
    From: "jrevens" <jrevens@comcast.net>
    I'm pretty sure that this has been brought up before, but not sure if any answers were provided. I receive the Daily List Digest via email, and today's digest contained 9 messages. Following message number 9, from Charles Rogers, there were pages and pages and pages of unreadable "code". It takes a couple of minutes just to scroll through all of it. It seems to have been awhile since this has happened, but sometimes it happens frequently. Is this possibly an issue with my iPad, my ISP, etc., or does it originate with the sender? Does anyone else experience this? -------- John Evens Thorp T-18 N71JE (built &amp; flying) Kitfox SS7 N27JE (building) Read this topic online here: http://forums.matronics.com/viewtopic.php?p=473367#473367


    Message 3


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    Time: 01:57:30 PM PST US
    Subject: Re: Dual batteries or dual alternators?
    From: "Flying Patagonia" <tintiescobar@hotmail.com>
    Thanks! Do you have this diagram in better quality? It cant see very well.. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=473370#473370


    Message 4


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    Time: 03:46:58 PM PST US
    Subject: Re: Dual batteries or dual alternators?
    From: "Flying Patagonia" <tintiescobar@hotmail.com>
    Bob, or anybody else to help how to wire a dual EFII, into the Z-12 diagram...? Thanks! Read this topic online here: http://forums.matronics.com/viewtopic.php?p=473371#473371


    Message 5


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    Time: 06:38:54 PM PST US
    From: Alec Myers <alec@alecmyers.com>
    Subject: alternator whine
    Hi Bob and others, My 182 has a noticeable alternator whine, about 5kHz (Im guessing) at cruise rpm. I think its worse recently than it used to be. Where and what should I start investigating?


    Message 6


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    Time: 07:39:25 PM PST US
    Subject: Re: alternator whine
    From: "user9253" <fransew@gmail.com>
    Check the AC (Alternating Current) component of the alternator output. If it is more than 1 volt, suspect a bad diode. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=473379#473379


    Message 7


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    Time: 10:05:09 PM PST US
    From: Bob Verwey <bob.verwey@gmail.com>
    Subject: Re: Voltmeter & Ammeter normal ranges
    Absolutely facinating and insightful to a neophyte like myself <grin> On 05 Oct 2017 7:17 PM, "Robert L. Nuckolls, III" < nuckolls.bob@aeroelectric.com> wrote: > At 08:32 AM 9/24/2017, you wrote: > > Exactly. Joe could you please confirm that the jpeg below is visible? If > so it's obvious that while the voltage seems to be moving around a tiny > bit, it never gets to the point which would allow the amperage shown. It's > always above 14V. Also I checked some data with the engine shut down and > while the amperage still wanders around it's 1 A or less (-5.5 to -6.5 A) > > > Digital data acquisition is fraught with > opportunity for confusion/error. Depending > on how the variable is sampled, pre-filtered > and software filtered, data displayed or plotted > can take on the appearance of instability. > > Unless you're measuring the output from something > like a battery . . . or a laboratory power supply, > the stimulus being observed will have some noise > on it. This is especially true of signals gathered > from the DC power system of any vehicle. > > When I'm gathering data on relatively low frequency > events, my DAS pre-filtering is usually rolled > off at 10 Hz. Then interpretation software is > designed to do a 'rolling average' on sampled values. > For a DAS set up to gather 100 samples/second, we'll > buffer 16 samples in a memory stack, take the sum > of those values then divide by 16 for an average > of that 'packet' of data. When the next sample comes > in, we add the new value, throw away the oldest value > and do the average again. > > This pre/post processing of data does a nice job > of ignoring the high frequency perturbations that > are riding on top of the value of interest. The > processed data plots are nice smooth lines that > are more meaningful. > > I suspect that data plots taken from most > EIS systems have little pre-processing and no > post processing . . . so the traces are understandably > 'ragged'. So while the voltage traces might > be interpreted as 'unstable', it's probable > that the system is operating normally. > > Just for grins, I took the 'scope out to peek at > the 14v bus in Dr. Dee's '87 GMC Sierra. With > the 'scope set to 2.5S/div H and 2V/div V, we > get the following trace when cranking the engine. > [image: []] > > Figure 1. > > Note that battery voltage starts to sag from > about 12.8 volts but takes a steeper slope > as the starter contactor is energized followed > by a profound drop to 8 volts as the contactor > closes. A few milliseconds later, the voltage > rises to about 10v until the engine catches > approx 1.2S later and the alternator kicks > in . . . whereupon but bus rises to about > 14.6V > > [image: []] > Figure 2. > > In the next plot we see that the bus is 'steady' > at about 14.7V with the occasional perturbation > combined with some little 'spikes' with an amplitude > of 1 to 2 volts. > > To get a closer look at the voltage in the > next plot, we need to turn up the 'scope sensitivity > and to to AC coupling: > > [image: []] > Figure 3. > > With a vertical scale of 0.5V/div and horizontal > of 0.05S/div we can get a better look at the 'noise'. > This particular trace caught a 1.5v transient amongst > about 10 smaller artifacts. > > We see that even when there are no obvious > transients, the horizontal line has 'thickness'. > Zooming in closer: > > [image: []] > Figure 4. > > We find that the horizontal line is 'fuzzy' with > positive and negative going transients on the > order of 300mV peak. > > Depending on where your digital data acquistion > system takese a 'snapshot', the sampled votlage > might appear to 'wobble' by as much as +/-0.5V. > > Spreading out the major transients by a factor > of 20 . . . > > > [image: []] > Figure 5. > > > Shows that they're about 400 microSeconds wide. These > plots offer a small peek into the nature of DC power > systems on vehicles. A few weeks ago, a thread on > another list server offered this image suggesting > that the full-wave, rectified 3-phase alternator > would produce wave forms something along these lines . . . > > [image: []] > > Figure 6. > > Theoretically true, but I've never seen so 'clean' > a picture in the wild . . . > > Referring to Mil-Std-704 we learn that DC power systems > demonstrate a certain amount of noise (distortion) > under normal conditions. The document cites > the following plot for a 28v system (cut the > numbers in half for 14 volts). > > [image: []] > > Figure 7. > > Over the range of 1000 Hz (1 milliSecond period) and > 10,000 Hz (100 uSecond), we should expect artifacts > of noise up to 0.5 VRMS (1.5 volts pk-pk) on a 14V bus. > > Above and below those frequencies, the allowable/exoected > noise levels fall off. When you hook an oscilloscope to > the bus, the best you can do is sample small features > of the noise as illustrated in the first 5 figures. Further, > you'll never see the pristine plots hypothesized in Figure 6. > > > [image: Emacs!] > Figure 8. > > The most significant attribute of a DC power system is VOLTAGE. > Referring again to Mil-STD-704 we find the plot above. Again, > cut the voltage levels in half for a 14v system. > > This figure suggests that any voltage vs. time condition > below the upper trace . . . and above the lower trace . . . > is a condition to be expected for designing and operating > appliances powered from the DC system. > > It's my wish that this narrative will give you some tools > for critical review of any data presented by either operating > or diagnostic instruments. Understanding characteristics > signals present on the bus -AND- limits on the measuring > instrument will go to better design, operation and diagnosis > of your ship's DC power system. > > Bob . . . >




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